feat: add CLI argument handling and build script

- Added command-line argument parsing to accept input file path instead of hardcoded value
- Added build task to compile standalone executable with deno compile
- Added usage message for incorrect invocation

deno.json

@@ -1,6 +1,7 @@
 {
   "tasks": {
-    "dev": "deno run --watch --allow-run --allow-write --allow-read src/main.ts"
+    "dev": "deno run --watch --allow-run --allow-write --allow-read src/main.ts",
+    "build": "deno compile --allow-run --allow-write --allow-read --output dist/dvdsubconvert src/main.ts"
   },
   "imports": {
     "@std/assert": "jsr:@std/assert@1"